The present invention relates in general to a universal tool for inspecting objects such as composite tubular objects and the like for locating various defects therein, and more particular, to a universal tool having a compact array of ultrasonic transducers arranged for the testing of various welds of such tubular objects, such as nuclear reactor vessels and components thereof, having different radii of curvature for detection of weld defects therein, for example, cracks, voids and the like.
Nuclear reactor vessels used in the commercial generation of electrical power are of two types, namely, the pressurized and boiling water type. In either case, the reactor vessel is constructed of a generally cylindrical metallic shell having a base and top flange welded thereto. The main shell portion itself is usually constructed of a series of lesser cylinders welded to each other along circumferential and longitudinal seams. In addition, a plurality of circumferentially spaced nozzles extend through the main shell and are likewise welded to the shell wall. Thus, numerous welds are necessarily used in fabricating the reactor vessel, in securing the top flange to the main shell, and in securing various injection inlet and outlet nozzles to the wall of the cylindrical shell of the reactor vessel. Typically, these welds are referred to as top flange welds, nozzle welds, nozzle safe end welds, ligament areas, i.e., the area between the stud holes of the top flange, circumferential welds and longitudinal welds.
These numerous welds, in particular their weld area and/or volume are, of course, inspected prior to the reactor vessel's initial use. Such inspection is carried out with all portions of the reactor vessel relatively accessible to an inspection tool or tools prior to its permanent installation. However, in-service inspection of the reactor vessel weld area and/or volume is not only desirable, but is mandated under certain government regulations. Under such regulations, it is required that each of the reactor vessel weld volumes be subjected to periodic volumetic examination whereby the structual integrity of the vessel is monitored. As required by such regulations, the top flange welds, nozzle welds, nozzle safe end welds and ligament areas are to be inspected at forty month periods, while the inspection of the circumferential and longitudinal welds of the vessel are conducted at ten year periods. To this end, there is disclosed in U.S. Pat. Nos. 4,196,049 and 4,170,891, which patents are assigned to the same assignee of the present invention, a tool for use in connection with making such inspections and which includes an ultrasonic transducer array for conducting the examination of the various weld volumes of the reactor vessel and its component parts at the forty month and ten year periods.
The foregoing prior art transducer array or tool is generally comprised of a relatively large rectangular support plate, typically 26 inches by 18 inches, having a plurality of individual ultrasonic transducers movably mounted thereon. The transducers, which include an ultrasonic transmitter and receiver, are each mounted to the support plate between a pair of outwardly extending guide rails which permit for the adjustable positioning of the transducers relative to one another on the support plate. In addition, the transducers are individually adjustable for emitting an ultrasonic beam at a predetermined angle relative to the support plate for penetrating the weld volume to be inspected at an angle mandated by the government regulations. Typically, the inspection angles required by these regulations are nominal angles of 45.degree. and 60.degree. with respect to a perpendicular to the examination surface, however, a tolerance of .+-.2.degree. is generally permitted.
In order to obtain the correct inspection angle for each of the ultrasonic transducers when inspecting a specific reactor vessel, it has been the prior art practice that each such transducer be individually positioned and that its orientation angle with respect to the support plate be individually adjusted prior to conducting an examination. In this manner, the transducers of the foregoing tool have been randomly positioned at a variety of individually calculated angles in order to meet the government regulations. However, such random positioning of these transducers has resulted in the need for a relatively large support plate which has rendered inspection of various reactor vessels cumbersome by the inability of the support plate to be manipulated effectively within the reactor vessel being inspected, as well its component parts, such as the attached nozzels. Further, the added weight of the support plate resulting from its size has further hindered the ability to effective manipulate the prior art tool in an optimum manner.
In addition to the undesirable size and weight of the prior art tool, such tool could not be used directly for inspection of reactor vessels and nozzles of different size, that is, those having different radii of curvature. For example, there is generally known three sizes of nuclear reactor vessels commonly referred to as the two-loop, three-loop and four-loop vessel and such vessels typically have different internal diameters, for example, diameters of 132 inches, 155 inches and 172 inches. As the examination surface of each of these reactor vessels have a different radius of curvature, it has been required that the orientation angles and position of the plurality of individual transducers of the prior art tool be individually adjusted for the weld inspection of each reactor vessel or component part having a different diameter. For example, a separate tool has been provided for the inspection of reactor vessels at the forty month period and one for the ten year period.
In using such tools, the relative position of the transducers has required adjustment via the guide rails, as well as adjusting their orientation angle relative to the support plate in order to accommodate the diameter of the reactor vessel being examined and the corresponding radius of curvature of the examination surface. Unless such repositioning and alignment of the individual transducers were performed, these prior art tools could not inspect reactor vessels of varing diameter while meeting the government regulations, for example, having nominal inspection angles of 45.degree. and 60.degree.. Although the precise location of the individual transducers and their orientation angles with respect to the support plate can be determined by computer analysis, it has been required that these transducers be individually positioned and aligned by hand. This hand positioning and alignment of the individual transducers often consumed as much as two man days resulting in inefficient use of the prior art tool, as well as additional expense when performing inspection of reactor vessels of different size.
Accordingly, it can be appreciated that there is an unsolved need for a universal tool for inspecting tubular objects such as vessels and the like, in particular, reactor vessels and their component parts, for locating various defects such as cracks and voids in the various weld volumes while being independent of the reactor vessel size, and while still meeting government regulations mandated for such testing.